Cathode ray tube gun having nested electrode assembly



SEARCH 00M May 31, 1966 R. H. HUGHES CATHODE RAY TUBE GUN HAVING NESTED ELECTRODE ASSEMBLY 4 Sheets-Sheet 1 Filed July 6, 1962 INVENTOR. flaw/m0 Hue/155 y 1966 R. H. HUGHES 3,254,251

CATHODE RAY TUBE GUN HAVING NESTED ELECTRODE ASSEMBLY Filed July 6, 1962 4 Sheets-Sheet 2 INVENTOR. lac/Mk0 A! Hum/:25

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y 1, 1966 R. H. HUGHES 3,254,251

CATHODE RAY TUBE GUN HAVING NESTED ELECTRODE ASSEMBLY Filed July 6, 1962 4 Sheets-Sheet 5 IN V EN TOR. F/(fi/Akp H HUG/IE3 y 31, 1966 v R. H. HUGHES 3,254,251

CATHODE RAY TUBE GUN HAVING NESTED ELECTRODE ASSEMBLY Filed July 6, 1962 4 Sheets-Sheet 4.

United States Patent 3,254,251 CATi-IODE RAY TUBE GUN HAVING NESTED ELECTRODE ASSEMBLY Richard Henry Hughes, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed July 6, 1962, Ser. No. 208,017 9 Claims. (Cl. 31370) This invention relates to cathode ray tubes and to electron guns therefor. The invention is particularly directed to cathode ray tubes having a unitary assembly comprising a plurality of electron guns disposed sideby-side for projecting and converging a plurality of electron beams on to a luminescent screen. Such electron gun assemblies are, for example, used in direct view color cathode ray picture tubes of the shadow mask type for home television use.

It is an object of this invention to provide new and improved means such as a plural electron gun assembly of the type described for generating a plurality of electron beams.

It is also an objected of this invention to provide a plural gun assembly having new and improved beam forming electrodes and arrangement thereof whereby said assembly is compact both axially and laterally, is rugged, provides the desired electron optics, beam shielding from stray electrostatic fields, and shadowing of electrode insulator supports from deposit of vaporized conductive materials, and is structurally simple and economical to manufacture.

Another object of this invention is the provision of a plural gun assembly which includes new and improved beam forming electrode design and arrangement which is especially suited for combination with a cathode assembly of the type which is supported from a plurality of elongated insulator rods independently of the beam forming electrodes.

Another object of this invention is the provision of an electron gun structure which includes a new and improved cathode assembly of the type described in which change of a pre-established cathode-grid spacing with repeated operation of the tube is reduced.

Features of this invention may, for example, be embodied in a plural electron gun assembly wherein each of the electron guns includes, in the order named, axially aligned cathode, control grid, screen grid, focus, and anode electrodes which are mounted in fixed relationship along a plurality of elongated insulator support rods. In a preferred embodiment of the invention, the plural gun assembly includes three similar guns disposed in delta array symmetrically about the central longitudinal axis of the cathode ray tube. Electrodes of the three guns are mounted on three glass support rods, each of which is disposed alongside a different two of the three guns. Each electrode is supported by members extending therefrom which are fixed to two of the support rods. A dynamic convergence cage, mounted on the anodes, includes a plurality of pairs of plate-like pole pieces, each pair of which straddles the beam path of one of the electron guns.

According to one feature of this invention, a cathode support member, control grid, and screen grid comprise apertured plates having integral bent-over tabs along two straight sides thereof which extend outwardly therefrom at an angle to each other into fixed contact with the insulator support rods.

According to another feature of the invention, the cathode sleeve is supported from the apertured cathode support plate by a support sleeve into which the cathode is disposed in concentric spaced relationship. The support sleeve is dimpled radially inwardly adjacent to one end thereof at a plurality of circumferentially spaced points and fixed to the cathode sleeve thereat.

The various features may be employed singly or in combination.

In the drawings:

FIG. 1 is a partial longitudinal section view with parts broken away of a cathode ray tube embodying the invention;

FIG. 2 is an enlarged perspective of one of the electron gun electrodes of the tube of FIG. 1;

FIG. 3 is an enlarged section view of the electron gun assembly of the tube of FIG. 1 taken along line 3-3 thereof;

FIG. 4 is an enlarged section view of the electron gun assembly taken along line 44 of FIG. 3;

FIG. 5 is a detail of a portion of FIG. 3 showing one of the cathode assemblies thereof;

FIG. 6 is an enlarged perspective view of the combination beading stamp and lateral convergence pole piece of the electron gun assembly of FIG. 1;

FIG. 7 is an enlarged transverse section of the electron gun and lateral convergence assemblies of FIG. 1 taken along line 77 thereof;

FIG. 8 is an enlarged section view of the electron gun and dynamic convergence assemblies of FIG. 1 taken along line 8-8 thereof; and,

FIG. 9 is an enlarged section of a portion of the convergence cage assembly of FIG. 8 taken along line 9--9 thereof.

In FIG. 1, by way of example, the invention is shown as embodied in a direct view color cathode ray picture tube 10 of the shadow mask type. The tube 10 comprises an envelope which includes a neck 12, a funnel 13, a faceplate 14, and a stem structure 15. A plurality of lead-in pins 16, over which an indexing wafer base 17 is disposed, are sealed through the stem 15. A mosaic dot phosphor screen 18, which may be aluminized according to known practices, is disposed on the inner surface of the faceplate 14. An apertured shadow mask 20 having an array of apertures therethrough, which is related to the array of phosphor dots of the mosaic screen 18, is mounted adjacent to the screen. Means in the form of a unitary electron gun assembly 22 comprising three substantially identically electron guns is disposed in the neck 12 and adapted to project three separate electron beams through a beam deflection zone 24 toward the mosaic screen 18. A magnetic deflection yoke 25 is provided for establishing beam deflection field in the deflection zone 24. As shown, for example, in FIGS. 3, 7, and 8, the electron guns of the assembly 22 are disposed symmetrically about the central longitudinal axis of the tube 10 in an equilateral trianguler (delta) array. In FIG. 1 only two of the three guns are shown.

Each of the three guns comprises a cathode assembly 26, a control grid 27, a screen grid 28, a focus electrode 29, and an anode 30, all of which are mounted in axially aligned spaced relationship along three insulator, e.g., glass, support rods 32. As shown in FIGS. 3 and 7, each of the insulator rods 32 are disposed along side a different two of the three electron guns outwardly therefrom. Only one of these rods is shown in FIG. 1. The focus electrodes 29 are supported from the rods 32 by combination support straps and lateral convergence pole pieces 34 as hereinafter described with reference to FIGS. 6 and 7. The anodes 30 are supported from the rods 32 by nonmagnetic straps 35 similar in shape to the pole piece straps 34. The cathode assembly 26, control electrode 27, and screen grid electrode 28 are supported from the rods 32 by integral strap-like tabs 42 as hereinafter described with reference to FIGS. 2, 3, and 4.

Heater filaments 48 for the cathodes are supported by a sectioned ring-shaped strap 50 mounted on the insulator support rods 32.

A dynamic electron beam convergence cage 44 1s mounted on the anodes 3t) and cooperates with external magnet means 46 to maintain convergence of the three electron beams at all times during their scanning of a raster on the luminescent screen 18. The construction and operation of the dynamic convergence arrangement is hereinafter more fully described with reference to FIGS. 8 and 9.

The lead-in conductors 16 are connected by connections (not shown) to the filaments 48, the cathode assemblies 26, the control electrodes 27, the screen grid electrodes 28, and the focus electrodes 29 of the electron guns. An electrical conductive coating 52 on the inner wall of the funnel 13 extends from the luminescent screen 18 into the neck 12 where it makes contact with a plurality of spring bulb-spacing elements 54. An ultor potential applied to the coating 52 through a lead-in terminal in the funnel wall in the funnel 13, schematically illustrated by the arrow 56, is thus applied to the anodes 30, the convergence cage 34, and the luminescent screen 18.

Referring to FIG. 2, each screen grid 28 comprises a sector-shaped plate portion 60, formed with an electron beam aperture 62 and an annular boss 64 (FIG. 4) concentric therewith. The sector-shaped member is bounded primarily by two straight sides or edges which are at an angle with each other and an edge between the spacedapart ends of the straight sides which may be straight, curved, or a combination of both, the curved edge being shown by way of example only. The two electrode support straps 42 are provided as bent-up tabs, integral with the sector-shaped plate portion 60 along the two sectorforming straight sides, or edges, 66 thereof. The tabs 42 extend beyond the outer arcuate edge 68 of the sectorshaped plate and terminate in a plurality of shaped projections 69 for anchoring the tabs in the support rods 32.

The illustration of the screen grid 28 in FIG. 2 is also representative of the general shape of control grid 27 and a support plate 70 (FIG. 4) of the cathode assembly 26. The control grid 27 is identical to the screen grid 28 except for the shape and size of the electron beam aperture therein. The cathode support plate 70 differs from the grid electrodes 27 and 28 primarily in that its sectorshaped plate portion 60 is provided with a large cathodereceiving aperture in place of the small electron beam aperture 62 and annular boss 64. The cathode support plate 70 is also made slightly smaller overall than the grid electrodes 27 or 28 so that it will nest with the control grid electrode 27 as hereinafter described with reference to FIGS. 3 and 4.

In a three gun assembly, such as the assembly 22, the sector-forming straight sides 66 of the cathode support plate 70 and of the beam forming grid electrodes 27 and 28 are at an angle of approximately 120 with each other. Thus, three of the same type electrodes, e.g., the control grid electrodes 27, may be compactly disposed back-toback in the fabrication of a three-gun, delta-arrayed electron gun assembly. Such back-to-back disposition is also illustrated in FIG. 3.

Should it be desired to fabricate, say, a four gun assembly, then the sector-shaped electrodes would be formed such that their sector-forming straight sides 66 would make an angle of approximately 90 with each other. This would permit four such electrodes to be disposed back-to-back.

Referring to FIGS. 3, 4, and 5, the cathode assembly 26 comprises the sector-shaped apertured cathode support plate 70, a cathode support sleeve 72, and a tubular cathode 74. The cathode support plate 70 has a large aperture 76 in the sector-shaped plate portion 6% thereof. The cathode support sleeve 72 is provided with an outwardly extending, axially-stepped, radial flange 78 and is disposed through the aperture 76 with the outermost portion of the flange 78 contiguous with the sector-shaped plate portion 60. The cathode 74 comprises a tubular sleeve having a coated, thermionically emissive transverse end wall 80. The cathode 74 is disposed in concentric spaced relationship within the support sleeve 72 with its open end adjacent to the distal end of the support sleeve. As best shown in FIGS. 4 and 5, the distal end of the support sleeve 72 is provided with three equally circumferentially spaced dimples 82, which extend inwardly into contact with the cathode sleeve 74. The cathode 74 is welded to the support sleeve 72 at the inward extremities of the dimples 82.

The cathode sleeve 74 preferably consists of a metal having good electron emissive properties, for example, nickel or a high nickel-content alloy. The cathode support sleeve 72 preferably consists of a low thermal conductivity metal such as a nickel-iron alloy. The cathode sleeve 74 and the cathode support sleeve 72 may thus be of dissimilar metals. Thus, when the cathode assembly is heated, during operation of the tube, the cathode 74 may tend to thermally expand radially more than does the cathode support sleeve 72. However, by virtue of the dimpled cathode supporting arrangement of the present structure, a unique and desired yieldable action at the junction of the cathode and support sleeve is provided. This action permits the cathode support sleeve 72 to be distorted radially outward by the expanding cathode 74 without the support sleeve exceeding its elastic limit. Thus, when the cathode assembly is cooled, the cathode support sleeve 72 will return to its original size.

In cathode assemblies wherein the cathode support sleeve is necked down in a circumferentially continuous mannerin contrast to the spaced dimpled arrangement of the present structure-the expanding cathode may stretch the cathode support sleeve beyond its elastic limit and thus introduce a permanent set thereinto. Such a permanent set will cause the pre-established cathode-grid spacing to be undesirably changed.

FIGS. 3 and 4 show the unique nesting relationship of the cathode support plate 70 with the control grid 27. As best shown in FIG. 3, the cathode support plate 70 is made slightly smaller than the control grid 27 so that it can nest within the control grid 27. The novel structure of these electrodes which permits such a nesting also permits the corresponding nested elements of the other two guns to be closely spaced therefrom in a backto-back relationship. This results in a close spacing of the axes of the three guns from each other and thus contributes to lateral compactness of the electron gun assembly 22.

The novel shape of the control grid 27 and cathode support plate 76 also contributes to the obtaining of axial compactness while simultaneously aifording rigidity for both electrodes and good thermal isolation of the cathode. By virtue of the cupless shape of the control grid 27, the cathode support sleeve 72 can be supported from its end adjacent the emissive end 80 of the cathode by relatively short support straps anchored in the support rods 32. Supporting of the cathode support sleeve 42 from this end results in the maximum length of thermal conduction path between the emissive end 80 (where the thermionic emissive temperature is maintained) and the point where the thin walled support sleeve 72 is mounted to the relatively massive support plate 70. This maximum separation along the length of the tubular cathode 74 and then back along the length of the support sleeve 72, in turn results in maximum thermal isolation of the emissive end 80 from those gun assembly parts, e.g., the support plate 70 and the insulator support rods 32 which could serve as a heat sink to absorb heat from the cathode 74. Rigidity of the cathode assembly results since the support straps from the cathode support plate 70 are short tabs 42 which extend directly toward the support rods 32. If the control grid were provided as a cup, the support straps from the cathode support plate 70 would have to extend axially along the cathode assembly 26 and around the open end of the grid cup.

From FIG. 4 it will be noted that whereas both the cathode support plate 70 and control grid 27 nest together and have their integral support tabs 42 extending toward the stem end of the tube 10, the screen grid 28 is disposed in axially reversed relationship thereto. That is, the integral support tabs 42 of the screen grid 28 extend toward the luminescent screen end of the tube 10. Accordingly, the sector-shaped plate portions 60 of the control grid 27 and the screen grid 28 are disposed in face-to-face relationship closely spaced to each other.

FIG. 4 also best illustrates the differences of form in the sector-shaped plate portions 60 of the cathode support plate 70, the control grid 27, and the screen grid 28. The control grid 27 is provided with an aperture 84 which, like the aperture 62 in the screen grid electrode 28, is of electron beam dimensions. In the embodiment illustrated, the control grid aperture 84 is, however, slightly smaller than the screen grid aperture 62 and is coined. That is, the plate portion 60 surrounding the aperture 84 is made thinner than the rest of the plate 60. In contrast to the electron beam apertures 62 and 84, the aperture 76 in the cathode support plate 70 is substantially larger so as to receive the cathode support sleeve 72 therethrough.

The annular boss 64 of the screen grid 28 extends toward the focus electrode 29, and as such forms a cup-shaped convergent electrostatic field between the screen grid 28 and the focus electrode 29. This field serves to prefocus the electron stream as it diverges from a first crossover in the vicinity of the screen grid aperture 62. Such prefocusing of the beam reduces the required strength of the main focus lens between electrodes 29 and 30, reduces the diameter of the beam in the main focus lens thus reducing the effects of lens distortion, and reduces the diameter of the beam at the center of deflection thus increasing the color purity tolerance when the gun is used with a polychrome mosaic phosphor screen.

The boss 64 of the control grid 27 serves a double function. It shields the region between the cathode emissive end 80 and the control grid aperture 34 from stray electrostatic fields. Such fields may be created from electrical connectors extending from the lead-in pins 16 to the screen grid 28 or the focus electrode 29. The boss 64 on the control grid 27 also serves to shadow portions of the insulator support rods 32 from deposit of sublimed material from the cathode sleeve 74. Such deposit, if allowed to form on the insulator rods 32, reduces the electrical resistance between electrodes and contributes to high resistance leakage.

It should be noted that if the control grid boss were not provided, then the control grid would have to be provided as a cup in order to obtain the desired shielding and shadowing mentioned above. But if this were done, as in the prior art, the cylindrical wall of the con-- trol grid cup would interfere with the supporting of the cathode support sleeve 72, as hereinbefore described.

FIGS. 6 and 7 illustrate the mounting of the focus electrodes 29 on the insulator support rods 32 and the lateral beam deflection convergence arrangement provided thereby. Each of the three focus electrodes 29 is mounted on a separate combination support strap and lateral convergence magnetic pole piece 34 made of mag netic material.

As shown in FIG. 6, the combination support straps and lateral convergence pole pieces 34 comprise a central arcuate electrode-receiving section 86 and two end sections 88. The end sections 88 are bent so as to extend in different directions at an angle of approximately 120 with each other. The end sections 88 are provided with E- shaped cutouts to produce a plurality of projections 90 which can be embedded in the insulator support rods 32.

As shown in FIG. 7, the three magnetic support-strappoles 34 are disposed in a somewhat triangular array with the ends of each strap being adjacent an end of a different strap and with these ends being embedded in the three insulator support rods 32. The three support-strap poles 34 are so disposed that the concave side of their arcuate electrode-receiving sections 86 face outwardly. The three tubular focus electrodes are thus mounted on the straps 34 on the outer facing sides thereof, that is, outside of the triangular array of the straps. Because the electrodes are disposed outside the triangular array of the straps 34, the straps serve to magnetically isolate the three electrodes 29 from each other.

As shown in FIG. 7, magnetic means 92 is provided externally of the neck 12 of the cathode ray tube for cooperation with the three support-strap-poles 34. The magnetic means 92 includes as its basic components, two bar magnets 94, which are disposed with like polarity poles substantially adjacent two of the apexes 95 of the triangular array of straps 34. Their opposite polarity poles are disposed radially outward therefrom. The bar magnets 94 may be either or both, permanently magnetized or electromagnetized by a pair of solenoids 96. The bar magnets 94 together with their solenoids 96 are retained in place by a magnetic strap 98 which is apertured near its ends to receive the bar magnets 94. The retaining strap 98 extends between the magnets 94 with at least a portion thereof disposed adjacent the tubular electrode 29 which is on the opposite side of the assembly 22 from the other apex 99 of the triangular array of straps 34. The retaining strap 98 is preferably contiguous with the neck 12. The retaining strap 98 is held on the neck 12 by a tension spring 100.

By virtue of the cooperative arrangement of the magnets 94 and the support strap poles 34, magnetic circuits are established as illustrated by the flux lines 102, 104 and 106. Flux created by the magneto 94 enter the ends of the straps 34 along paths 102. A portion of the flux is conducted by the upper strap toward the upper focus electrode 29 and then passes through space along the paths 104 to the retaining strap 98 through which it is conducted back to the magnets 94. The other portion of the flux is conducted by the lower straps 34 to the vicinity of the two lower focus electrodes 29 and thence pass through space along the paths 106 to the retaining strap 98 through which it is conducted back to the magnets 94. The direction of flux flow through the upper focus electrode is in a direction opposite to that through the two lower focus electrodes. Thus, the electron beam passing through the upper focus electrode will be deflected in one lateral direction while the electron beams passing through the two lower focus electrodes will be deflected in the opposite lateral direction. By virtue of such opposite lateral deflections, maximum convergence sensitivity is obtained as described in U.S. Patent 2,847,- 598, issued on August 12, 1958 to R. H. Hughes.

In the event that the lateral convergence correction required is opposite that which would be provided by the magnet arrangement shown in FIG. 7, the magnets 94 can be reversed in the retaining strap 98. The flux flow and hence the lateral beam deflection will thus be opposite that illustrated.

Although the magnets 94 are shown disposed exactly, radially outward from the apexes 95, they may instead be slightly shifted circumferentially around the neck 12 from the apexes 95 so as to obtain a desired shaping of the magnetic fields within the tubular electrodes 29. Arrangements wherein the magnets 94 are described as disposed circumferentially adjacent the apexes 95 are meant to include arrangements in which the magnets 94 are so shifted.

The solenoids 96 may be energized either with a suitable time varying current or by direct current so that the lateral convergence may be either dynamically or statically provided.

FIGS. 8 and 9 illustrate the tube structure and external magnet means for providing dynamic radial convergence. Such convergence is known in the art and will therefore not be described in detail herein. A description of dynamic radial convergence may be found in the Hughes patent cited above and in US. Patent 2,752,520, issued on June 26, 1956 to A. M. Morrell.

As shown in FIGS. 8 and 9, the convergence cage 44 of tube comprises a cup 110 having a cylindrical wall 112 and an end wall 114. A Y-shaped magnetic shield 115 divides the cup 110 into three equal parts. The end wall 114 is provided with three apertures 116, one in each of the three divisions of the cup 119, through which the electron beams from the three electron guns pass. The cylindrical wall 112 is provided with six longitudinal slots through which three pair of pole pieces 118 are dis posed. Each pole piece 118 includes a plate-like element 119 and a flange 128. The plate-like elements 119 of each pair of pole pieces 118 are substantially parallel to each other and straddle the beam path of one of the electron guns. The flange 120 of each pole piece 118 lies along the external surface of the cylindrical wall 112. The flange 1249 includes alternate flush and raised portions. The spaced-apart flush portions 122 and 124 are contiguous with or lie flush with the cylindrical wall 112 and are welded thereto. The spaced-apart raised portions 126 and 128 are substantially parallel to but spaced from the cylindrical wall 112 and are disposed very close to the neck 12.

By virtue of this close spacing, maximum sensitivity of coupling between the pole piece 118 and the external magnet 46 is obtained. On the other hand, since the flush portions of the flange which are welded to the cylindrical wall 112 are recessed from the neck 12, weld splash which might exist on the flange in the form of sharp peaks, is safely spaced from the conductive coating 52 on the neck 12. Were the coating 52 to be scratched by weld splash peaks on the flange 120, portions of the coating might be scraped-off and remain as harmful debris in the finished cathode ray tube 10. The flush and raised portions of the flange 120 tend to prevent such scrape-off.

One of the raised portions 128 extends beyond the axial extent of its associated plate-like element 119. Thus the coupling between the external magnet 46 and the pole piece 118 is not limited by the axial length of the plate like element 119.

What is claimed is:

1. A cathode ray tube including an electron gun assembly comprising a plurality of substantially similar electron guns mounted on a plurality of insulator support rods, each of said guns including an electrode comprising a sector-shaped, apertured plate portion and a pair of bent-over tabs integral therewith along the sector-forming straight sides thereof, said electrodes of said guns being compactly juxtaposed to each other in back-to-back relationship with their tabs facing each other and extending outwardly from said guns into fixed relationship with said support rods.

2. A cathode ray tube including a plural gun assembly comprising a given number of substantially similar electron guns each comprising a plurality of axially aligned electrodes mounted along a plurality of insulator support rods, each electrode of one set of corresponding electrodes of said guns comprising a sector-shaped apertured plate and bent-over tabs integral therewith along the sectorforming straight sides thereof, said tabs lying in planes at an angle to each other, said angle being of a size substantially equal to 360 divided by said given number, said set of electrodes being compactly juxtaposed to each other in back-to-back relationship with their tabs facing each other and extending outwardly into fixed relation- Ship with said support rods.

3. A cathode ray tube including a plural gun assembly comprising a plurality of electron guns each of which includes a pair of nested electrodes mounted on a plurality of insulator support rods, each of said nested electrodes of each gun comprising a sector-shaped plate and bent-over tabs integral therewith along the sector-forming straight sides thereof, said nested electrodes being similarly oriented and juxtaposed in nested relationship with their tabs extending outwardly therefrom into fixed relationship with said support rods.

4. A cathode ray tube including a plural gun assembly comprising a plurality of electron guns each of which comprises a plurality of axially aligned electrodes mounted along a plurality of insulator support rods, each of an adjacent two of said electrodes of each gun comprising a sector-shaped plate and bent-over tabs integral therewith along the sector-forming straight sides thereof, said tabs lying in planes at an angle to each other, said angle being substantially the same for each of said two electrodes, one of said two electrodes being slightly smaller overall than the other, said two electrodes being similarly oriented and juxtaposed in nested relationship with each other, said tabs extending outwardly from said guns into fixed relationship with said support rods.

5. A cathode ray tube including an assembly comprising a plurality of electron guns each of which includes axially spaced control grid and screen grid electrodes mounted along a plurality of insulator support rods, each of said electrodes comprising a sector-shaped plate and a pair of bent-over tabs integral therewith along the sector-forming straight sides thereof, said control grid and screen grid of each gun being oppositely oriented and juxtaposed with corresponding surfaces of their sectorshaped plates disposed face-to-face with each other and with their said tabs extending outwardly from said guns and in opposite axial directions into fixed relationship with said support rods.

6. A cathode ray tube including a plural gun assembly comprising a plurality of electron guns each of which comprises a plurality of axially spaced electrodes including a cathode, a control grid, a screen grid, and a focus electrode mounted along a plurality of insulator support rods, each of said control grid and said screen grid of each of said electron guns comprising an apertured sectorshaped plate and a pair of bent-over tabs integral therewith along the sector-forming straight sides thereof, said plate portion having an annular bossed ridge concentrically surrounding the aperture therein, the bossed ridge of said control grid extending toward said cathode and surrounding the region between said cathode and the aperture of said control grid to shield said region from stray electrostatic fields and to shadow portions of said support rods from said cathode, the bossed ridge of said screen grid extending toward said focus electrode for forming a cup-shaped convergent electrostatic field therewith, said control grid and said screen grid of each gun being oppositely oriented and juxtaposed with corresponding surfaces of their sector-shaped plate portions disposed face-to-face with each other and with their said tabs extending outwardly from said guns and in opposite axiial directions into fixed relationship with said support ro s.

'7. A cathode assembly comprising a tubular cathode sleeve having an electron emissive surface at one end and a tubular cathode support sleeve of larger diameter than said cathode sleeve disposed concentrically therewith, said cathode support sleeve being dimpled inwardly at a plurality of circumferentially spaced points and fixed to said cathode sleeve thereat.

8. A cathode assembly comprising an apertured cathode support plate, a tubular cathode support sleeve which has an outward radial flange at one end thereof and which is disposed concentrically within the aperture of said apertured cathode support plate with said flange fixed to said support plate, and a tubular cathode sleeve of smaller diameter than said cathode support sleeve disposed concentrically within said cathode support sleeve and said cathode support plate aperture in radially spaced relationship therewith, said cathode sleeve having one end closed and coated with electron emissive material, said cathode support sleeve being dimpled inwardly adjacent the other end thereof at a plurality of circumferentially spaced points which are welded to said cathode sleeve adjacent its other end.

9. A cathode ray tube including an electron gun assembly comprising a plurality of substantially similar electron guns, each of which includes a cathode assembly and a control grid adjacent thereto mounted along a plurality of insulator support rods, each of said cathode assemblies comprising an apertured cathode support plate, a tubular cathode support sleeve which has an outward radial flange at one end thereof and which is disposed concentrically within the aperture of said apertured cathode support plate with said flange fixed to said support plate, and a tubular cathode sleeve of smaller diameter than said cathode support sleeve disposed concentrically within said cathode support sleeve and said cathode support plate aperture in radially spaced relationship therewith, said cathode sleeve having a transverse wall at one end coated with electron ernissive material, said cathode support sleeve being dimpled inwardly adjacent the other end thereof at a plurality of circumferentially spaced points which are fixed to said cathode sleeve adjacent its other end, said cathode sleeve exhibiting a greater thermal radial expansion than said cathode support sleeve at their fixed together ends during operation of said tube, each of said cathode support plates and said control grids comprising an apertured sector-shaped plate and bent-over tabs integral with said plate along the sector-forming straight sides thereof, the said cathode support plate and the said control grid of each of said guns being similarly oriented and nested together, the control grids of said electron guns being juxtaposed to each other in back-to-back relationship with their tabs facing each other and extended outward therefrom in fixed relationship with said insulator support rods.

References Cited by the Examiner UNITED STATES PATENTS 2,436,265 2/1948 Pohle et al. 313-85 2,752,520 6/ 1956 Morrell 313- 2,778,966 1/1957 Faustini et al. 313-82.1 X 2,808,527 10/1 957 McKenzie 313-270 X 2,847,598 8/1958 Hughes 313-70 2,849,646 8/1958 Noskowicz 31392.5 X 2,861,208 11/1958 Benway 313-70 2,886,729 5/1959 May 313- 2,888,588 5/1959 Dichter 313-82.1 2,897,390 7/1959 Jensen 313-77 2,898,493 8/ 1 959 Burdick 313-77 2,914,694 11/1959 Chin 313-337 X 2,991,381 7/1961 Hughes 313-84 3,004,183 10/1961 Levin 31382.1 3,024,380 3/1962 Burdick et al. 313-70 3,085,1175 4/1963 Knauf 313-270 3,128,407 4/ 1964 Mattson 313-270 X 3,145,318 8/1964 Paull 313-270 X GEORGE N. WESTBY, Primary Examiner.

ROBERT SEGAL, C. O. GARDNER,

Assistant Examiners. 

7. A CATHODE ASSEMBLY COMPRISING A TUBULAR CATHODE SLEEVE HAVING AN ELECTRON EMISSIVE SURFACE AT ONE END AND A TUBULAR CATHODE SUPPORT SLEEVE OF LARGER DIAMETER THAN SAID CATHODE SLEEVE DISPOSED CONCENTRICALLY THEREWITH, SAID CATHODE SUPPORT SLEEVE BEING DIMPLED INWARDLY AT A PULARALITY OF CIRCUMFERENTIALLY SPACED POINTS AND FIXED TO SAID CATHODE SLEEVE THEREAT. 